Display apparatus

ABSTRACT

A display apparatus of the type which forms a color image by modulating a plurality of lights different from each other in color by one or more display elements, includes a device for changing the color purity of at least one light by inserting or extracting a wavelength selection element into or out of the optical path of at least one of the plurality of lights, or changing the attitude of the wavelength selection element, and a device for supplying information as to whether the wavelength selection element is in the optical path of the at least one color light or information on the attitude of the wavelength selection element in the optical path of the at least one color light.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a display apparatus, such as aprojection type display apparatus for displaying computer images, videoimages, etc. on a large screen.

2. Description of the Related Art

Recently, the purposes of use of projection type display apparatuses fordisplaying computer images in presentations using computers arediversified, and there is a demand for a projection type displayapparatus which provides optimum color purity, color balance,illuminance, etc. according to the purpose of use.

FIG. 8 shows the construction of a conventional projection type displayapparatus. In FIG. 8, white light emitted from a light source portion101 is condensed by a reflector 102, passes through fly-eye lenses 103and 104, a polarization transformation element 105, and a condenser lens106. Then, it travels by way of a mirror M1 and is separated into threecolor lights of R, G and B by dichroic mirrors DM1 and DM2, transmittedthrough condenser lenses 107G and 107B and a relay lens system 107R,transmitted through dichroic filters DF(G) and DF(R), and transmittedthrough image display elements 108R, 108G and 108B before the colorlights of R, G and B are synthesized into one, the image displayed onthe image display elements being projected in an enlarged state onto ascreen or the like (not shown) by a projection lens 109.

As the light source, a discharge lamp such as a metal halide lamp or amercury vapor lamp is used. FIG. 9 shows an example of the spectraldistribution of a white light source.

As shown in FIG. 9, generally speaking, a white light source has acontinuous intensity distribution in the visible light wavelength rangeof 400 nm to 700 nm. In a projection type display apparatus as shown inFIG. 8, this white light is separated into color lights of R, G and B ina color separation system. At this time, when light component in thewavelength range of 570 nm to 600 nm is taken in the green color lightcomponent, the green is turned into yellow, making it difficult toexpress the pure green color.

Further, when light component in the wavelength range of 570 nm to 600nm is taken in the red color light component, the red is turned intoorange, making it difficult to express the pure red color. In view ofthis, in the illumination system of the projection type displayapparatus, a dichroic filter, etc. are provided on the incident side ofthe image display elements in addition to the dichroic mirrors DM1 andDM2 to remove the light of the wavelength range of 570 nm to 600 nm sothat the light of the wavelength range of 570 nm to 600 nm may not reachany of the image display elements. FIG. 10 shows the spectraldistribution of white light synthesized by a dichroic prism DP whenlight of the wavelength range of 570 nm to 600 nm is removed.

In the construction of FIG. 8, the spectral transmittances of thedichroic mirrors DM1 and DM2 are shown in FIGS. 11 and 12, and thespectral transmittances of dichroic filters DF(G) and DF(R) when lightof the wavelength range of 570 nm to 600 nm is removed by providing thedichroic filters DF(G) and DF(R) are shown in FIGS. 13 and 14. Here,there is a technique in which at least one of the dichroic filters DF(R)and the DF(G) can be inserted and removed into and from the optical pathmaking it also possible to display a color image with no dichroicfilter. According to this technique, the dichroic filter is inserted andremoved into and from the optical path to thereby vary the purity of thecorresponding color to vary the light quantity, whereby it is possible,in a single projection type display apparatus, to select between acolor-purity-emphasized (color-reproduction-emphasized) display form(normal mode) and a brightness-emphasized display form.

However, the construction in which the dichroic filter is inserted orremoved to thereby vary the purity of the corresponding color to varythe light quantity, has the following problems.

1. When a user of the projection type display apparatus has inserted orremoved the dichroic filter into or from the optical path, it ispossible for the user to recognize whether the apparatus is in thecolor-purity-emphasized mode or the brightness-emphasized mode. However,if after this user has inserted or removed the dichroic filter, anotheruser uses the projection type display apparatus to display an image fromwhich it is difficult to recognize whether the apparatus is in thecolor-purity-emphasized mode or the brightness-emphasized mode, theapparatus might be used in a state not suited for the purpose of use ofthe other user.

2. When the dichroic filter is removed from the optical path (when it ison standby outside the optical path), the quantity of light impingingupon the image display elements is larger than when the dichroic filteris in the optical path, so that the amount of heat generated at thepolarizing plates provided in front of and behind the image displayelements also substantially increases, with the result that thetemperature in the vicinity of the image display elements rises, therebyadversely affecting the characteristics of the image display elementsand the polarizing plates.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide adisplay apparatus capable of solving the above problems 1 and 2separately or simultaneously.

In a first aspect of the present invention, there is provided a displayapparatus of the type which forms a color image by modulating aplurality of lights different from each other in color, by one or moredisplay elements. The display apparatus comprising means for obtaining aplurality of different display forms by changing the color purity of atleast one of the plurality of lights, and means for supplyinginformation on the display forms.

In a second aspect of the present invention, there is provided a displayapparatus of the type which forms a color image by modulating aplurality of lights, different from each other in color, by one or moredisplay elements. The display apparatus comprising means for changingthe color purity of at least one of said plurality of lights byinserting or extracting a wavelength selection element into or out ofthe optical path of at least one of said plurality of lights or changingthe attitude of the wavelength selection element, and means forsupplying information as to whether the wavelength selection element isin the optical path of the at least one of the plurality of lights orinformation on the attitude of the wavelength selection element in theoptical path of the at least one of the plurality of lights.

In a third aspect of the present invention, there is provided a displayapparatus, wherein said means for supplying information includes adisplay means formed by an LED, a liquid crystal device, etc.

In a fourth aspect of the present invention, there is provided a displayapparatus of the type which forms an image by modulating light by one ora plurality of display elements, said display apparatus comprisingcooling means for cooling the display elements, the cooling means beingcapable of varying its cooling capacity according to variation in thedisplay form of the image.

In a fifth aspect of the present invention, there is provided a displayapparatus of the type which forms an image by modulating light by one ormore display elements, with the display apparatus comprising coolingmeans for cooling the display elements and means for varying thequantity of light impinging on the one or more display elements. Thecooling capacity of the cooling means with respect to the one or moredisplay elements is varied according to variation in the quantity oflight.

In a sixth aspect of the present invention, there is provided a displayapparatus of the type which forms a color image by modulating aplurality of lights, different from each other in color, by one or moredisplay elements. The display apparatus comprises cooling means forcooling the display elements and means for obtaining a plurality ofdisplay forms by changing the color purity of at least one light of theplurality of lights, wherein the cooling capacity of the cooling meansis varied with respect to the display elements modulating said at leastone of said plurality of lights according to variation in the colorpurity of at least one of said plurality of lights.

In a seventh aspect of the present invention, there is provided adisplay apparatus of the type which forms a color image by modulating aplurality of lights different from each other in color by one or aplurality of display elements. The display apparatus comprises coolingmeans for cooling the display elements and means for varying the colorpurity of at least one light of the plurality of lights by inserting orremoving a wavelength selection element into or from the optical path ofthe at least one light or varying the attitude of the wavelengthselection element. The cooling capacity of the cooling means withrespect to the display elements modulating said at least one light isvaried according to whether the wavelength selection element is in theoptical path of said at least one light or not or according to variationin the attitude of the wavelength selection element in the optical pathof said at least one light.

In an eighth aspect of the present invention, there is provided adisplay apparatus wherein the cooling means is an air cooling typecooling means, the variation in the cooling capacity being variation inair flow rate with respect to the display element.

In a ninth aspect of the present invention, there is provided a displayapparatus wherein the cooling means is a water cooling type coolingmeans, the variation in the cooling capacity being variation in flowrate with respect to the display element.

In a tenth aspect of the present invention, there is provided a displayapparatus of the type which forms a color image by modulating aplurality of lights, different from each other in color, by one or moredisplay elements. The display apparatus comprises air-cooling means forair-cooling the display elements, means for varying the color purity ofat least one light of the plurality of lights by inserting or removing awavelength selection element into or from the optical path of the atleast one light or varying the attitude of the wavelength selectionelement, and means for supplying information on the position or theattitude of the wavelength selection element with respect to the opticalpath of the at least one light. The air flow rate of the air-coolingmeans is varied with respect to the display elements modulating the atleast one light according to whether the wavelength selection element isin the optical path of the at least one light or not or according to theattitude of the wavelength selection element in the optical path of theat least one light.

In an eleventh aspect of the present invention, there is provided adisplay apparatus wherein said means for supplying information isprovided with means for detecting that the wavelength selection elementis in the optical path of said at least one light or that it is in apredetermined attitude and for lighting a lamp.

In a twelfth aspect of the present invention, there is provided adisplay apparatus wherein the wavelength selection element is an elementwhich transmits visible light of a wavelength longer than apredetermined wavelength and blocks visible light of a wavelengthshorter than that or an element which transmits visible light of awavelength shorter than a predetermined wavelength and blocks visiblelight of a wavelength longer than that.

In a thirteenth aspect of the present invention, there is provided adisplay apparatus wherein the wavelength selection element is an edgefilter, a band pass filter or a band cut filter.

In a fourteenth aspect of the present invention, there is provided adisplay apparatus comprising a plurality of dichroic mirrors separatingwhite light from a light source into the plurality of lights ofdifferent colors consisting of red, green and blue lights.

In a fifteenth aspect of the present invention, there is provided adisplay apparatus wherein the display elements are arranged incorrespondence with the red, green and blue lights, and wherein thereare provided a plurality of dichroic mirrors for synthesizing imagelight from a plurality of display elements modulating the red, green andblue lights.

In a sixteenth aspect of the present invention, there is provided adisplay apparatus wherein the display elements include three pixelgroups, respectively corresponding to the red, green and blue lights,and micro lens arrays condensing lights of the colors corresponding tothree pixels of each group.

In a seventeenth aspect of the present invention, there is provided adisplay apparatus further comprising a projection lens for projectingthe image of the display portions of the display elements onto a screen,a wall or the like.

In an eighteenth aspect of the present invention, there is provided aprojection type display apparatus comprising image display elements,alight source for illuminating the image display elements, at least onefirst optical element for color-separating the light from the lightsource into at least two color lights and causing them to impinge uponthe image display elements, at least one second optical element forsynthesizing the lights output from the image display elements into one,and a lens upon which the light from the at least one second opticalelement impinges and which projects the image displayed by the imagedisplay elements in an enlarged state. A third optical element whichtransmits visible light of a wavelength shorter than that or vice versa,can be inserted or removed in or from the optical path between the atleast one first optical element and the at least one second opticalelement, and there is provided means for supplying information as towhether the third optical element is in the optical path or not.

In a nineteenth aspect of the present invention, there is provided aprojection type display apparatus wherein the means for supplyinginformation as to whether the third optical element is in the opticalpath or not consists of means for detecting that the third opticalelement is in the optical path and indicating this by an indicatinglamp.

In a twentieth aspect of the present invention, there is provided aprojection type display apparatus comprising image display elements, alight source for illuminating the image display elements, a firstoptical element for color-separating the light from the light sourceinto at least two color lights and causing them to impinge upon theimage display elements, a second optical element for synthesizing thelights output from the image display elements into one, and a lens uponwhich the light from the second optical element impinges and whichprojects the image displayed by the image display elements in anenlarged state. A third optical element which transmits visible light ofa wavelength shorter than that or vice versa, can be inserted or removedin or from the optical path between the first optical element and thesecond optical element, and there is provided means for changing thecooling condition of the image display elements upon which a larger orsmaller quantity of light impinges according to whether the thirdoptical element is in the optical path or not.

In a twenty-first aspect of the present invention, there is provided aprojection type display apparatus wherein said means for changing thecooling state consists of a means for detecting the third opticalelement in the optical path and reducing the air flow rate of thecooling fan as compared to the condition in which the third opticalelement is not in the optical path.

In a twenty-second aspect of the present invention, there is provided animage processing apparatus comprising a display apparatus and a computer for inputting image information to said apparatus.

Further objects, features and advantages of the present invention willbecome apparent from the following description of the preferredembodiments (with reference to the attached drawings).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing an optical arrangement according to anembodiment of the present invention;

FIG. 2 is a diagram illustrating the color selection element holdingstructure in the embodiment;

FIG. 3 is a diagram illustrating the LED control portion of theembodiment;

FIG. 4 is a diagram illustrating the operation of the LED controlportion of the embodiment;

FIG. 5 is a diagram illustrating the control when the power source isturned on in the LED control of the embodiment;

FIG. 6 is a diagram illustrating the FAN control portion of theembodiment;

FIG. 7 is a diagram illustrating the operation of the FAN controlportion of the embodiment;

FIG. 8 is a diagram showing a conventional projection type displayapparatus;

FIG. 9 is a diagram showing the spectral distribution of a light source;

FIG. 10 is a diagram showing a spectral distribution color-synthesizedin a projection apparatus;

FIG. 11 is a diagram showing the spectral transmittance of an opticalelement in a projection apparatus;

FIG. 12 is a diagram showing the spectral transmittance of an opticalelement in a projection apparatus;

FIG. 13 is a diagram showing the spectral transmittance of an opticalelement in a projection apparatus;

FIG. 14 is a diagram showing the spectral transmittance of an opticalelement in a projection apparatus; and

FIG. 15 is a diagram showing a state in which control is effected suchthat an indication is given on a projection screen to the effect thatthe apparatus has been switched to a “brightness-emphasized” projectionstate.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows the optical arrangement of a projection type displayapparatus according to an embodiment of the present invention.

In FIG. 1, numeral 1 indicates a white light source, numeral 2 indicatesa reflector, numeral 3 indicates first fly-eye lens (lens array),numeral 4 indicates a second fly-eye lens (lens array), numeral 5indicates a polarization conversion element provided with a plurality ofpolarization separation layers 5 a, a plurality of reflection surfaces 5b, and a plurality of wavelength plates 5 c, and numeral 6 indicates acondenser lens.

Numerals DM1 and DM2 indicate dichroic mirrors, numerals M1 and M2indicate mirrors, and numeral SC1 indicates a wavelength selectionelement which is a color selection optical element that can be insertedand removed. The wavelength selection characteristic of the element SC1is the same as that of the dichroic filter DF(R) of FIG. 8. Instead ofthe element SC1, it is also possible to use the dichroic filter DF(G) ofFIG. 8 which is a color selection optical element that can be insertedand removed, or in addition to the element SC1, it is possible to usethe dichroic filter DF(G).

Further, this element SC1 is a so-called edge filter which transmitsvisible light of a wavelength longer than a predetermined wavelength butblocks light of a wavelength shorter than that or which transmitsvisible light of a wavelength shorter than a predetermined wavelengthbut blocks light of a wavelength longer than that. In the presentinvention, it is also possible to use a band pass filter or a band cutfilter as the wavelength selection element inserted or removed into orfrom the optical path of a light of a predetermined color to therebyvary the purity of the predetermined color to vary the quantity oflight. Japanese Unexamined Patent Application Publication No. 7-72450discloses an example in which this kind of wavelength selection elementis used to switch between color-purity-emphasized mode andbrightness-emphasized mode, and the construction of the optical systemof a projection type display apparatus using this type of wavelengthselection element can be understood by referring to the abovementionedofficial gazette, so a detailed description thereof will not be given inthe present invention. However, the control methods of the presentinvention are applicable to the display apparatus disclosed in thisofficial gazette.

In FIG. 1, numeral DF1 indicates a dichroic filter, numerals 7G and 7Bindicate condenser lenses, numeral 7R indicates a relay lens systemcomposed of lenses 71R, 72R and 73R and mirrors 74R and 75R, andnumerals 8G, 8R and 8B indicate image display elements.

Numeral DP1 indicates a dichroic prism, and numeral 9 indicates aprojection lens.

The dichroic mirrors DM1 and DM2 form the abovementioned at least onefirst optical element, the dichroic prism DP1 form the above-mentionedat least one second optical element, and the color selection opticalelement SC1 forms the above-mentioned third optical element andwavelength selection element.

The optical operation of this system will be described. White lightemitted from the light source 1 is condensed by the reflector 2, passesthrough the fly-eye lenses 3 and 4, the polarization conversion element5, and the condenser lens 6, and travels by way of the mirror M1 beforeit is separated into color lights of R, G and B. The color lights passmirror M2, the condenser lenses 7G and 7B, and the relay lens system 7R,and are transmitted through the image display elements 8R, 8G and 8Bbefore the color lights of R, G and B are synthesized into one by thedichroic prism DP1, and the image displayed on the image displayelements is projected onto a screen (not shown) in an enlarged state bythe projection lens 9. The lens system 7R is composed of lenses 71R, 72Rand 73R and mirrors 74R and 75R.

FIG. 2 shows an example of the holding structure for the color selectionoptical element SC1 of this embodiment. In this example, the colorselection optical element SC1 is fastened to a slidable guide 11, andthe user slides a knob 12 from outside the apparatus, whereby the colorselection optical element SC1 can be inserted or removed into or fromthe optical path. Further, there is provided a switch 13 to make itpossible to detect whether the color selection optical element is in theoptical path or not.

As a means for switching between color-purityemphasized mode andbrightness-emphasized mode by varying the purity of a predeterminedcolor by the color selection element to vary the quantity of light, itis possible to keep such an optical element in the optical path of apredetermined color and vary the inclination angle thereof with respectto the optical path (optical axis), apart from inserting or removing theoptical element in or from the optical path of the predetermined color(not necessarily a dedicated optical path).

FIG. 3 shows the construction of a control circuit for indicating theprojection state of this embodiment to the user.

Numeral 21 indicates a switch detection circuit, which detects a changein the ON/OFF state of the switch 13 to generate a detection signal.Numeral 22 indicates an LED control circuit for controlling the lightingof the LED on the basis of the detection signal from the detectioncircuit 21.

FIG. 4 is a flowchart illustrating the control flow when, during the useof the projection type display apparatus of this embodiment, the displayform is switched between the color-purity-emphasized display mode andthe brightness-emphasized display mode by the knob 12.

In Step 1, the detection circuit detects a change in the state of theswitch 13, and supplies a detection signal to the LED control circuitwhen the switch 13 is turned ON or OFF.

When, in Step 2, the state of the switch 13 is changed from OFF to ON,the procedure advances to Step 31, in which the LED comes on, and whenthe state of the switch 13 is changed from ON to OFF, the procedureadvances to Step 32 to turn off the LED.

While in the above-described embodiment the LED is lighted as anindication to the user, it is also possible, as shown in FIG. 15, toperform control such that an indication to the effect that the apparatushas been switched to the brightness-emphasized projection state (in FIG.15, the message “emphasis on brightness”) is given on the projectionscreen or the operating panel (liquid crystal display device) of theapparatus, or a voice message: “The apparatus has been changed to thebrightness-emphasized mode”, may be given to the user.

FIG. 5 is a flowchart illustrating the control flow of another form whenthe power source of the projection type display apparatus of thisembodiment is turned on.

When the power source is turned ON in Step 1, the switch detectioncircuit 21 detects the state of the switch 13 and generates a detectionsignal in Step 2. When the detection signal is ON in Step 3, the LED islighted in Step 4. When the detection signal is OFF, the LED is notlighted, and the procedure advances to the control of the state of useshown in FIG. 3.

FIG. 6 is a diagram showing the control system of a cooling fan which isan air cooling means. Numeral 21 indicates a switch detection circuit,which detects a change in the ON/OFF state of the switch 13 to generatea detection signal. Numeral 23 is a fan control circuit, which controlsthe air flow rate of the fan on the basis of the detection signal fromthe detection circuit 21.

FIG. 7 is a flowchart illustrating the control flow when the projectionstate is switched during the use of the projection apparatus.

In Step 1, the detection circuit detects a change in the state of theswitch 13, and supplies a detection signal to the LED control circuitwhen the switch 13 is turned ON or OFF.

In Step 2, when the state of the switch 13 is changed from OFF to ON,the procedure advances to Step 3, and the voltage applied to the fan isincreased so that the speed of the fan may be increased. When the stateof the switch is changed from ON to OFF, the procedure advances to Step32, in which the voltage applied to the fan is reduced so that the speedof the fan may be reduced.

While in this embodiment the air flow rate of the fan is increased ordecreased by controlling the speed of the fan, it is also possible toincrease or decrease the air flow rate by providing a backup fan, whichrotates when the color selection optical element is outside the opticalpath and does not rotate when the color selection optical element is inthe optical path.

While in the above-described embodiment the projection type displayapparatus is controlled according to the flows of both FIGS. 4 and 7, itis also possible, in the present invention, to provide two differentprojection display apparatuses that are controlled by the flow of eitherFIG. 4 or FIG. 7.

Further, while in the projection type display apparatus of thisembodiment an air cooling means is used as the means for cooling theimage display elements, it is also possible to use a water cooling meansfor cooling the image display elements by a water cooling system, withthe flow of the cooling fluid being varied according to whether thecolor selection optical element is in the optical path or not (The flowrate is increased when the color selection optical element is in theoptical path, and decreased when it is not).

Further, while the image display apparatus of the above-describedembodiment is a so-called three-plate type color image display apparatususing three image display elements, there is no limitation to the numberof image display elements in the present invention. For example, thepresent invention is also applicable to a projection type displayapparatus using a single color image display element. A form of thissort of projection type display apparatus has a micro lens array on theincident side, using image display elements (usually, liquid crystalpanels) of the type which condense lights of R, G and B on pixel groupscorresponding to the primaries of R, G and B by the micro lens array, acolor separation optical system, a projection lens and other opticalsystems but using no color synthesis optical system. The optical systemsof such projection type display apparatuses are disclosed, for example,in Japanese Unexamined Patent Application Publications No. 3-56922 and4-60538. By referring to these official gazettes and the aboveembodiment, the present invention can be easily applied to suchprojection type display apparatuses.

Further, in the present invention, the form of the image display elementis not restricted to a liquid crystal display device. It is alsopossible to adopt a form using a display element based on some otheroptical modulation principle.

Further, the present invention is not restricted to the front sideprojection type display apparatus shown in the drawings. The presentinvention is also applicable to a direct view type or a back sideprojection type display apparatus.

While the present invention has been described with reference to whatare presently considered to be the preferred embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments. On the contrary, the invention is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims. The scope of the following claims is to beaccorded the broadest interpretation so as to encompass all suchmodifications and equivalent structures and functions.

What is claimed is:
 1. A display apparatus of the type which forms animage by modulating light by one or more display elements, said displayapparatus comprising: cooling means for cooling the one or more displayelements; and means for varying the quantity of light impinging on theone or more display elements, wherein a cooling capacity of said coolingmeans with respect to the one or more display elements is variedaccording to a variation in the quantity of light.
 2. A displayapparatus of the type which forms a color image by modulating aplurality of lights, different from each other in color, by one or moredisplay elements, said display apparatus comprising: cooling means forcooling the one or more display elements; and means for obtaining aplurality of display forms by changing the color purity of at least onelight of the plurality of lights, wherein a cooling capacity of saidcooling means is varied with respect to the one or more display elementsmodulating the at least one light according to a variation in the colorpurity of the at least one light.
 3. A display apparatus of the typewhich forms a color image by modulating a plurality of lights, differentfrom each other in color, by one or more display elements, said displayapparatus comprising: cooling means for cooling the one or more displayelements; and means for varying the color purity of at least one lightof the plurality of lights by inserting or removing a wavelengthselection element into or from the optical path of the at least onelight or varying the attitude of said wavelength selection element,wherein a cooling capacity of said cooling means with respect to the oneor more display elements modulating the at least one light is variedaccording to whether said wavelength selection element is in the opticalpath of the at least one light or according to a variation in theattitude of said wavelength selection element in the optical path of theat least one light.
 4. A display apparatus according to one of claims 1,2 and 3, wherein said cooling means is an air cooling type coolingmeans, wherein the variation in the cooling capacity is a variation inan air flow rate with respect to the one or more display elements.
 5. Adisplay apparatus according to one of claims 1, 2, and 3, wherein saidcooling means is a water cooling type cooling means, wherein thevariation in the cooling capacity is a variation in a water flow ratewith respect to the one or more display elements.
 6. A display apparatusof the type which forms a color image by modulating a plurality oflights, different from each other in color, by one or more displayelements, said display apparatus comprising: air cooling means for aircooling the one or more display elements; means for varying the colorpurity of at least one light of the plurality of lights by inserting orremoving a wavelength selection element into or from the optical path ofthe at least one light or varying the attitude of said wavelengthselection element; and means for supplying information on the positionor the attitude of said wavelength selection element with respect to theoptical path of the at least one light, wherein an air flow rate of saidair-cooling means is varied with respect to the one or more displayelements modulating the at least one light according to whether saidwavelength selection element is in the optical path of the at least onelight or according to the attitude of said wavelength selection elementin the optical path of the at least one light.
 7. A display apparatus ofthe type which forms a color image by modulating a plurality of lights,different from each other in color, by one or more display elements,said display apparatus comprising: means for changing the color purityof at least one light of the plurality of lights by inserting orextracting a wavelength selection element into or out of the opticalpath of the at least one light or changing the attitude of saidwavelength selection element; and means for supplying information as towhether said wavelength selection element is in the optical path of theat least one light or information on the attitude of said wavelengthselection element in the optical path of the at least one light, whereinsaid means for supplying information is provided with means for (i)detecting that said wavelength selection element is in the optical pathof the at least one light or that said wavelength selection element isin a predetermined attitude and (ii) for lighting a lamp.
 8. A displayapparatus of the type which forms a color image by modulating aplurality of lights, different from each other in color, by one or moredisplay elements, said display apparatus comprising: means for changingthe color purity of at least one light of the plurality of lights byinserting or extracting a wavelength selection element into or out ofthe optical path of the at least one light or changing the attitude ofsaid wavelength selection element; and means for supplying informationas to whether said wavelength selection element is in the optical pathof the at least one light or information on the attitude of saidwavelength selection element in the optical path of the at least onelight, wherein the wavelength selection element is an element whichtransmits visible light of a wavelength longer than a predeterminedwavelength and blocks visible light of a wavelength shorter than that oran element which transmits visible light of a wavelength shorter than apredetermined wavelength and blocks visible light of a wavelength longerthan that.
 9. A display apparatus of the type which forms a color imageby modulating a plurality of lights, different from each other in color,by one or more display elements, said display apparatus comprising:means for changing the color purity of at least one light of theplurality of lights by inserting or extracting a wavelength selectionelement into or out of the optical path of the at least one light orchanging the attitude of said wavelength selection element; and meansfor supplying information as to whether said wavelength selectionelement is in the optical path of the at least one light or informationon the attitude of said wavelength selection element in the optical pathof the at least one light, wherein the wavelength selection element isan edge filter, a band pass filter or a band cut filter.
 10. A displayapparatus of the type which forms a color image by modulating aplurality of lights, different from each other in color, by one or moredisplay elements, said display apparatus comprising: means for changingthe color purity of at least one light of the plurality of lights byinserting or extracting a wavelength selection element into or out ofthe optical path of the at least one light or changing the attitude ofsaid wavelength selection element; and means for supplying informationas to whether said wavelength selection element is in the optical pathof the at least one light or information on the attitude of saidwavelength selection element in the optical path of the at least onelight. further comprising a plurality of dichroic mirrors for separatingwhite light from a light source into the plurality of lights ofdifferent colors, wherein the plurality of lights of different colorsconsists of red, green and blue lights.
 11. A display apparatusaccording to claim 10, wherein the display elements are arranged incorrespondence with the red, green and blue lights, and wherein thereare provided a plurality of dichroic mirrors for synthesizing imagelight from a plurality of display elements modulating the red, green andblue lights.
 12. A display apparatus according to claim 10, wherein theone or more display elements include three pixel groups, respectivelycorresponding to the red, green and blue lights, and a micro lens arrayscondensing lights of the colors corresponding to the three pixels ofeach group.
 13. A display apparatus of the type which forms a colorimage by modulating a plurality of lights, different from each other incolor, by one or more display elements, said display apparatuscomprising: means for changing the color purity of at least one light ofthe plurality of lights by inserting or extracting a wavelengthselection element into or out of the optical path of the at least onelight or changing the attitude of said wavelength selection element; andmeans for supplying information as to whether said wavelength selectionelement is in the optical path of the at least one light or informationon the attitude of said wavelength selection element in the optical pathof the at least one light, further comprising a projection lens forprojecting the image of display portions of the one or more displayelements onto a screen or a wall.
 14. A projection type displayapparatus comprising: image display elements; a light source forilluminating said image display elements; at least one first opticalelement for color-separating the light from said light source into atleast two color lights and causing them to impinge upon said imagedisplay elements; at least one second optical element for synthesizingthe lights output from said image display elements into one; and a lensupon which the light from said at least one second optical elementimpinges and which projects the image displayed by said image displayelements in an enlarged state, wherein a third optical element whichtransmits visible light of a wavelength longer than a predeterminedwavelength and blocks visible light of a wavelength shorter than that orvice versa, can be inserted into or removed from the optical pathbetween said at least one first optical element and said at least onesecond optical element, and wherein there is provided means forsupplying information as to whether said third optical element is in theoptical path.
 15. A projection type display apparatus according to claim14, wherein said means for supplying information as to whether saidthird optical element is in the optical path consists of means fordetecting that said third optical element is in the optical path andindicating this by an indicating lamp.
 16. A projection type displayapparatus comprising: image display elements; a light source forilluminating the image display elements; a first optical element forcolor-separating the light from said light source into at least twocolor lights and causing them to impinge upon said image displayelements; a second optical element for synthesizing the lights outputfrom said image display elements into one; and a lens upon which thelight from said second optical element impinges and which projects theimage displayed by said image display elements in an enlarged state,wherein a third optical element which transmits visible light of awavelength longer than a predetermined wavelength and blocks visiblelight of a wavelength shorter than that or vice versa, can be insertedinto or removed from the optical path between said first optical elementand said second optical element, and wherein there is provided means forchanging a cooling condition of said image display elements upon which alarger or smaller quantity of light impinges according to whether saidthird optical element is in the optical path.
 17. A projection typedisplay apparatus according to claim 16, wherein said means for changingthe cooling condition comprises means for detecting if said thirdoptical element is in the optical path and reducing an air flow rate ofthe cooling fan as compared to a condition in which said third opticalelement is not in the optical path.
 18. An image processing apparatuscomprising a display apparatus as claimed in one of claims 1, 2, 3, 6,7, 8, 9, 10, 13, 14, and 16 and a computer for inputting imageinformation to said display apparatus.